The present invention relates to a capacitor, especially to a solid capacitor that increases the capacity by means of larger surface area of the dielectric layer thereof. Moreover, the solid capacitor in accordance with the present invention can be stacked repeatedly so as to form a multilayer capacitor.
A capacitor is an energy storage component applied in circuits for tuning, filtering, coupling, by-pass, energy conversion and delay. Most common used capacitors are electrolytic capacitors, mica capacitors, ceramic capacitors and vitreous-enamel capacitor. The names refer to the type of dielectric that is used within the capacitor.
capacitor typesstructure and featuresaluminumAn aluminum cylinder works as aelectrolyticcathode with liquid electrolyte thereincapacitorand a curved aluminum piece is used asan anode. The flow of direct currentcauses an insulating metal oxide togrow out of and into the surface of theanode. The metal oxide is used asdielectric. The advantage ofelectrolytic capacitors is the highcapacity per unit volume. Thedisadvantage of electrolyticcapacitors is the non-ideal, lossycharacteristics and poor stability. It isused for signal coupling. In usage,please note that the voltage should notbe applied in the reverse direction.paper capacitorTwo metal foils as electrodes areclipped on insulated paper and theassembly can be rolled up to form acylinder that is enclosed inside a metalhousing or insulated material such assealing wax, ceramic orvitreous-enamel. The package issmaller with higher capacitance. Dueto high inherent inductance and loss ofcapacitor, the device is suitable forbeing applied to low frequency circuit.metallizedThe device basically has the samepaper capacitorstructure with paper capacitors while ametal membrane is used instead ofmetal foil. Its features are smallvolume and higher capacitance,generally applied to low-frequencycircuit.oil impregnatedBy impregnating the paper with specialpaper capacitoroil, tolerance of the capacitor isimproved. It features on high capacityand wide tolerance. However, thevolume of the device is quite large.vitreous-enamelThe dielectric material iscapacitorvitreous-enamel. It has advantages ofceramic capacitors while the volume issmaller. It withstands hightemperature.ceramicThe dielectric is ceramic and thecapacitorplates are made from ceramic base withsilver membrane. Its features are smallvolume, good thermostability, higherinsulation resistance but low capacity.Thus it is used for high frequencycircuit. The ferroelectric ceramiccapacitor has higher capacity while theloss and temperature coefficient arehigher. Thus it is applied to lowfrequency circuit.film capacitorThis capacitor has the same structurewith the paper capacitor. Thedielectric of the capacitor is polyesteror polystyrene. The polyestercapacitor has higher dielectricconstant, small volume, high capacity,and good stability thus is suitable forbypass capacitors. While thepolystyrene capacitor has small loss,high insulation resistance but hightemperature coefficient. Thiscapacitor is suitable for highfrequency circuit.mica capacitorThe silver electrodes or metal foil areplated directly onto the micadielectric. Several layers ofelectrodes and mica are laminated andthen are cast inside the phenolic resinor sealed inside the epoxy. Itsproperties are low loss of dielectric,high insulation resistance, lowtemperature coefficient and it issuitable for high frequency circuit.tantalum orTantalum or niobium is used asniobiumpositive electrode and diluted sulfuricelectrolyticacid works as negative electrode whilecapacitordielectric is oxide membrane onsurface of the tantalum or niobium. Ithas small volume, high capacity,stable performance, long life, highinsulation resistance, and goodthermostability. Thus it is applied toequipments with higher requirementsof capacitors.semi-variableIt's also called trimmer capacitor. Thecapacitordevice consists of two pieces or twosets of metal spring with dielectrictherebetween. The distance or areabetween two metal springs changeswhile tuning. The dielectric can be air,ceramic, mica or membrane.variableIt is constructed by a set of immobilecapacitorpates called stator, and another set ofplates, connected to a common axis,called rotor and its capacity changesaccording to rotation of the rotor. Thetwo-fold capacitors are two capacitorswhose rotors share the common axis.The dielectric of such capacitor can beair or polystyrene. Capacitors with airdielectric with features of largevolume and small loss are used in theelectron tube radios. The variablecapacitor with polystyrene dielectricis a compact sealed capacitor, mostlyused in the transistor radio.
Solid capacitors with dielectric layer made from ceramic material with high dielectric constant have features of environmental protection, low impedance, high thermostability, withstanding high ripple current and high reliability. Compared with traditional electrolytic capacitors, solid capacitors have higher stability thus explosion may occur less frequently.
The most common solid capacitor is multilayer ceramic capacitor (MLCC) manufactured by suspending ceramic powders in liquid and casting into a thin green sheet with thickness from 20 um to 5 um or even thinner. Then metal electrodes are sieved(screen) printed onto the sheets which are later stacked with sheets without electrodes alternately to form a laminated structure. After being sintered at high temperature, the device becomes a ceramic sinter that provides an extremely high capacity in a small volume. At last, surface of silver terminal electrode is plated with nickel, tin and lead and then the multilayer ceramic is soldered directly onto the printed circuit board.
The present invention provides a solid capacitor that improves disadvantages of electrolytic capacitors and increases capacity.